1. Field of the Invention
The present invention relates to a method of manufacturing a friction speed change gearing of a type which comprises a housing, first and second rotary shafts rotably supported in said housing in axial alignment with each other, an inner race supported by said first rotary shaft, an outer race supported by said housing to be co-axial with said inner race, a plurality of cylindrical rollers mounted between said inner and outer races subject to an elastic deformation, and a spider member supported by said second rotary shaft to engage said rollers in a manner to allow them to freely rotate around their own axes and to drive or to be driven by said rollers when they make a planetary movement.
2. Description of the Prior Art
In the aforementioned friction speed change gearings, when said first rotary shaft is rotated by an outer driving power, the driving torque is transmitted to said second rotary shaft in a speed changing manner (in a speed reducing manner in this case) by way of said plurality of cylindrical rollers which make a planetary movement in an annular space defined by said outer and inner races and said spider member engaging said rollers.
In manufacturing a friction speed change gearing of this type, when said rollers are mounted in said annular space, they must be somewhat deformed or compressed in a diametrical direction. However, it is difficult to insert the relatively small cylindrical rollers into said annular space while compressing them in a diametrical direction and there is a danger that the rollers are damaged or distorted during such an inserting process thereby causing a problem that the friction speed change gearing does not provide an expected performance in operation.
In dealing with this problem, it has been proposed in Japanese Patent Application No. 53901/71 filed by the same assignee as that of the present application to manufacture a friction speed change gearing of this type by first forming a pre-assembly of said first rotary shaft, inner race, rollers, outer race, spider member, and second rotary shaft and secondly pressing the pre-assembly into a bore of the housing, wherein said bore is formed to have an inner diameter which is a little smaller than the outside diameter of said outer race so that said outer race is contracted when it has been pressed in said housing bore, thereby applying an elastic pre-stressing to said rollers, or by first preparing a pre-assembly of said first rotary shaft, etc., inserting said pre-assembly into a bore of the housing having an inner diameter which is larger than the outer diameter of said outer race and finally pressing an annular wedging member into an annular space left between said housing bore and said outer race, thereby contracting said outer race so as to apply an elastical prestressing to said rollers.